Alkoxysiloxanols

ABSTRACT

ALPHA-ALKOXY-OMEGA-SILOXANOLS, R&#39;&#39;O(R2SIO)XH, ARE PRODUCES BY CONTACTING CYCLIC SILOXANES WITH ALCOHOLS UNDER MILD CONDITIONS. FOR EXAMPLE HEXAMETHYLCYLOTRISILOXANE HEATED AT REFLUX IN METHANOL FOR FOUR HOURS GIVES 5- METHOXYHEXAMETHYLTRISILOXAN-1-OL IN HIGH YIELD. THE REACTION PROCEEDS MORE RAPIDLY IN THE PRESENCE OF WEAK ACIDS OR BASES. THE PRODUCTS ARE USEFUL AS ANTISTRUCTURE AGENTS COUPLING AGENTS, AND FILLER-TREATING AGENTS FOR SILICONE ELASTOMERS.

United States Patent 3,799,962 ALKOXYSILOXANOLS Richard Newton Lewis,Tecumseh, Mich, assignor to Stauffer Chemical Company No Drawing. FiledDec. 30, 1971, Ser. No. 214,406 Int. Cl. C07f 7/18 US. Cl. 260-448.8 R12 Claims ABSTRACT OF THE DISCLOSURE Alpha-alkoxy-omega-siloxanols,R'O(R SiO),,H, are produced by contacting cyclic siloxanes with alcoholsunder mild conditions. For example, hexamethylcyclotri siloxane heatedat reflux in methanol for four hours gives 5methoxyhexamethyltrisiloxan-l-ol in high yield. The reaction proceedsmore rapidly in the presence of weak acids or bases. The products areuseful as antistructure agents, coupling agents, and filler-treatingagents for silicone elastomers.

This invention relates to alkoxysiloxanols and more particularly toalpha-alkoxy-omega-siloxanols. Such materials contain one relativelymore reactive group (OH) and one relatively less reactive group(alkoxy); for this reason they have long been sought as intermediates inthe synthesis of siloxanes. They have not, however, been available byany process known heretofore.

Several processes that might have been expected to lead toalkoxysiloxanols have instead produced other products. For example,linear and cyclic methylpolysiloxanes heated with methanol in thepresence of potassium hydroxide gave instead trimethylalkoxysilanes anddimethyldimethoxysilanes (*U.S. Pats. 2,746,982 and 2,826,599). Cyclictrisiloxanes heated with n-octyl alcohol and toluenesulfonic acid inxylene gave dioctyloxytrisiloxanes and water as the principal products,even when the reaction was stopped at an early stage. [See Sprung and'Guenther, J. Org. Chem. 26, 552 (1961)].

It is an object of this invention to provide alkoxysiloxanols. Anotherobject of this invention is to provide alpha-alkoxy-omega-siloxanols. Itis also an object of this invention to provide a method of producingalpha-alkoxyomega-siloxanols in high yield and in a high state ofpurity. It is a further object of this invention to provide novelantistructure agents, coupling agents and fillertreating agents.

These objects, and others which will become apparent from the followingdescription, are achieved, generally speaking, by contacting a cyclicpolysiloxane with an alcohol having up to 20 carbon atoms underrelatively mild conditions to form a compound of the general formulaRO(R SiO) H, wherein R and R are organic radicals and x is an integer ofat least 2 and preferably from 2 to 10. In some cases satisfactoryresults are obtained without a catalyst. In other cases it isadvantageous to employ a weak base or a weak acid as a catalyst.

The cyclic polysiloxanes that may be used in the practice of thisinvention have the general formula (R SiO) The radicals represented by Rin this formula are hydrocarbon radicals, halogenated hydrocarbonradicals or cyanoalkyl radicals having from 1 to 8 carbon atoms.Suitable radicals include alkyl radicals such as methyl, ethyl, propyl,butyl or hexyl and fluorinated derivatives thereof; alkenyl radicalssuch as vinyl or allyl; and aryl radicals such as phenyl or tolyl andchlorinated derivatives thereof. It is preferred that at least half ofthe radicals be methyl radicals. Very good results are obtained if allof the radicals are methyl.

The number of units, y, in the cyclic polysiloxane is at least 3 and maybe as high as 10. Generally the fastness and cleanest reaction occurswhen y is 3. However, very good results are also obtained when y is 4 or5 or even more. Suitable cyclic polysiloxanes thus include those of thegeneral formula [(CH SiO] where y is from 3 to 10, particularly when yis 3, 4 or 5. Other cyclic polysiloxanes that may be used include thosehaving groups other than methyl; for example,

trimethyltrivinylcyclotrisiloxane,tetramethyltetravinylcyclotetrasiloxane,heptamethylvinylcyclotetrasiloxane, trimethyltriethylcyclotrisiloxane,trimethyltriphenylcyclotrisiloxane, hexaphenylcyclotrisiloxane,

and the like.

Alcohols of almost every description may be used in the practice of thisinvention. Long-chain or short-chain alkyl, cycloalkyl, alkenyl andaralkyl alcohols and substituted derivatives thereof having up to 20carbon atoms, including allyl alcohol and benzyl alcohol may be used.Substituted alcohols such as ethanolamine, 2-methoxyethanol, and2-chloroethanol may also be used. Best results are usually obtained withthe short-chain primary and secondary alcohols having up to 4 carbonatoms, e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, or isobutylalcohol. The cleanest and fastest reactions, with fewest side reactions,occur with methyl alcohol.

The general reaction may be expressed by the equation In this equation Rrepresents the radical of an alcohol having up to 20 carbon atoms.Generally x is equal to y. Under certain conditions, x may have valuesgreater than or less than y. It is preferred to work with a large excessof the alcohol, or the reaction may be very slow. Mole ratios of alcoholto cyclic polysiloxane should be between 221 and 50:1, preferably atleast 5:1. Ratios higher than 50:1 may be employed, but olfer no specialadvantage.

Reaction temperature is not critical. A reasonable rate of reaction canusually be achieved at room temperature or below. Often it is preferredto operate at somewhat higher temperatures, but generally not much overC. The reflux temperature of the alcohol is often a satisfactoryoperating temperature. If higher temperatures are desired, the reactionsmay be conducted under moderate pressure, but this is not usuallynecessary.

In some instances, as in the reaction of methanol with a cyclictrisiloxane, no catalyst is required, and the reaction proceeds at asatisfactory rate at the reflux temperature of the methanol.

When a catalyst is desired a weak acid or a weak base may be added, asindicated above. Strong acids such as toluenesulfonic acid and strongbases such as sodium methoxide are completely unsatisfactory as theycause unwanted cleavage and equilibration reactions. Even moderatelystrong acids such as oxalic acid (pK 1.23) cause rapid decomposition ofthe alkoxysiloxanol that is produced and are of borderline utility. Foroptimum utility the catalyst should have a pK, or pK above 1.5,corresponding to an acid or basic dissociation constant below 0.03.Maleic acid (pK 1.83) and phosphoric acid (pK 2.12) are about thestrongest acids that can be used with safety. Even so they must bequickly neutralized when the desired reaction has been essentiallycompleted. In general, any organic or inorganic acid or base may be usedif its pK or pK lies between 1.5 and 10. Extremely weak acids or baseswith pK values above 10 are relatively ineffective.

In order to eliminate the neutralization step, it is advantageous to usean acid or base that is volatile, so that it can be removed bydistillation. A catalyst that decomposes into harmless by-products onheating is also desirable. Suitable acid catalysts include formic acid(pK 3.75),

acetic acid (pK, 4.75), propionic acid (pK 4.87), malonic acid (pK2.83), succinic acid (pK 4.16), and cyanoacetic acid (pK 2.45).

Suitable bases include the primary, secondary, and tertiary aliphaticamines, which have pK values in the range of about 1.95(diisopropylamine) to 4.26 (trimethylamine); ammonia (pK 4.75);ethanolamine and its alkyl derivatives; pyrrolidine, piperidine, andtheir homologs; morpholine (pK 5.4), N-methylmorpholine (pK 6.5), andN-ethylmorpholine (pK 6.2); ethylenediamine (pK 4.07) and its n-alkylderivatives; piperazine (pK 4.1)

and dimethylpiperazine (pK 5.8); pyridine (pK 8.77); and aromatic aminessuch as dimethylamine (pK 8.94). Ammonia and the more volatile aminesare particularly preferred because of their easy removal.

Salts of weak acids and bases may also be used, but they are less easilyremoved than the acids and bases listed above, and are therefore notusually preferred.

The catalysts listed above are effective at relatively lowconcentrations. Concentrations up to five percent may be used, but thepreferred range is from 0.01 to 1.0 percent.

In order to purify the alkoxysiloxanols the excess of alcohol is removedby distillation at atmospheric or reduced pressure. Unreacted cyclicpolysiloxane, if any, is best removed by vacuum distillation. Thealkoxysiloxanol left in the distillation pot at this stage is oftenenough for most purposes. Further purification, if desired, may beachieved by distilling the alkoxysiloxanol at reduced pressure. Productsof essentially 100 percent purity can thus be obtained.

The alkoxysiloxanols of this invention are useful as chemicalintermediates, as antistructure agents in silicafilled elastomers, andas agents for reducing the surface reactivity of inorganic fillers,especially siliceous fillers. Suitably treated fillers may be obtainedby heating untreated fillers with alkoxysiloxanols, preferably in therange of 50 to 200 C. The hydrophobic fillers thus obtained are veryuseful in the preparation of high-strength silicone elastomers.

Alkoxysiloxanols that contain vinyl groups, e.g.methoxytrimethyltrivinyltrisiloxan-l-ol, are particularly useful ascoupling agents between inorganic materials such as fillers and fibrousreinforcing agents, e.g. glass fibers, and organic polymers, especiallythose that are cured by free-radical or vinyl-addition reactions.Examples include silica-reinforced elastomers of various types andglassreinforced polyesters.

The following examples are oifered by way of illustration, but not byway of limitation. In these examples the dimethylsiloxane unit, (CH Si0,is represented by the symbol D, and the methylvinylsiloxane unit, CH C HSiO, is represented by the symbol D". All parts are by weight unlessotherwise specified.

EXAMPLE 1 Hexamethylcyclotrisiloxane (D (22.2 parts) was dissolved in120 parts of methanol and heated at reflux for hour hours. Analysis bygas chromatography showed, in addition to methanol, 91.0 percent5-methoxy-hexamethyl trisiloxan-l-ol (CH OD H), 7.5 percent unreacted Dand 1.5 percent 3-methoxy-tetramethyldisiloxan-1-ol (CH OD H), thelatter indicating a slight amount of additional cleavage of thetrisiloxanol. There was no evidence of symmetrical siloxanes such as adimethoxytrisiloxane or a trisiloxanediol. On distillation at reducedpressure a nearly pure fraction of CH OD H was obtained boiling at 86 C.(15 mm.). Absorption in the near infrared showed strong, sharp OH peaksat 2700 nm. and 2900 nm. Nuclear magnetic resonance showed the groupratios CH (Si) 6.0, CH O 1.1, OH 1.0; theoretical 6:1:1.

EXAMPLE 2 Ten parts of 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane (Dwas mixed with 70 parts of methanol and 0.35 part of formic acid andallowed to stand at room temperature for 4 days. The methanol was thenremoved under vacuum below room temperature, and the remainder wasdistilled at 1.6 mm, giving 8.1 parts of a product boiling at 78-89 C.Analysis by gas chromatography of the product showed 7.6 percent of3-methoxy-l,3-dimethy1-1,3-divinyl-disiloxan-1-ol (CH OD H), 21.5percent of D;,, 68.9 percent of S-methoxy-1,3,5-trimethyl-1,3,5-trivinylsiloxane-l-ol (CH OD H), and 2.0 percent of CH OD H.

EXAMPLE 3 Octarnethylcyclotetrasiloxane (D (11 parts) was heated toreflux with 60 parts of methanol and 0.4 part of formic acid for 16hours. Gas chromatographic analysis showed 29.7 percent of7-methoxyoctamethyltetrasiloxanl-ol. (CH OD H), 1.0 percent of of CH ODH, 0.1 percent of CH OD H, 68.7 percent of unreacted D and 0.5 percentof a volatile compound, possibly CH ODH. The rate of formation of CH ODH is thus about 2 percent per hour at 65 C., with very little byproduct.

EXAMPLE 4 One part of decamethylcyclopentasiloxane (D was mixed with 6parts of methanol and 0.07 part of cyanoacetic acid and kept at roomtemperature for 48 hours. At the end of this time 6.7 percent of the Dhad been converted to 9 methoxydecamethylpentasiloxane 1 ol (CH OD H)with no byproducts detectable at a level of 0.02 percent. This is aconversion of 3.4 percent per day.

A similar reaction was carried out with 0.15 part of di-n-butylamine. Asmaller amount of CH OD H was produced, along with significant amountsof OH OD H, CH OD H, and CH OD H. In this example the acid catalystappears to give fewer byproducts.

EXAMPLE 5 One part of D was mixed with 7 parts of ethyl alcohol and 0.05part of for-mic acid at room temperature. In six hours gaschromatography showed the following (in addition to ethyl alcohol):unreacted D, 71.0 percent, C H OD H 18.3 percent, a more volatilebyproduct 3.8 percent, and a less volatile byproduct 6.9 percent.

EXAMPLE 6 Eleven parts of D 60 parts of n-propyl alcohol and 0.4 part offormic acid were heated at reflux (95 C.) for one hour, producing amajor amount of C H- OD H and minor amounts of two less volatilematerials.

EXAMPLE 7 Eleven parts of D 60 parts of methanol, and 0.6 part of aceticacid were heated at reflux (65 for 2 hours. At this time 98 percent ofthe D had been converted to CH OD H, with only traces of by-products (CHOD H and CH OD H). In comparison with a similar reaction without acatalyst (Example 1) it is clear that the reaction in the presence ofacetic acid is not only faster but produces fewer by-products.

EXAMPLE 8 Example 7 was repeated with 0.4 part of formic acid in placeof acetic acid, and the reaction was about 96 percent complete in 12minutes, again with practically no by-products. When reflux wascontinued for 90 minutes, small amounts of CH OD H, CH OD H and CH OD Hwere formed.

EXAMPLE 9 Example 7 was repeated with 0.5 part ofN,N'-dimethylpiperazine as a catalyst. The reaction was percent completein 10 minutes with only traces of byproducts. After 2.5 hours of refluxsignificant amounts of CH OD H, CH OD H, CH OD H, and CH OD H wereformed, CH OD H still being the major product.

EXAMPLES 10-12 Solutions of 9 parts of D in 60 parts of methanol wereprepared at room temperature. To these were added 0.5

part of cyanoacetic acid, 0.15 part of ammonia, and 0.3 part ofdi-n-butylamine. All were efiective catalysts and produced 90 percentyields of CH OD H in less than 30 minutes. In each case significantbyproducts appeared only after several hours.

Identification of the minor ingredients in the above Examples 1-12 wasmade on the basis of gas chromatography. A Varian Aerograph Model 700Gas Chromato graph was used. The column used has the followingdescription:

Material: Stainless steel Dimensions: 5 feet x inch O.D.

Liquid phase: Dimethyl silicone gum (SE-30), 30 percent.

Solid support: 70-80 mesh acid-washed dimethyldichlorosilane-treatedfirebrick (Gas-chrom RZ), 70 percent.

Helium flow: 60 ml./min.

The reaction times given below are those actually measured. They werereproducible within 1 percent using the above column, although anothercolumn might have given somewhat different values. However, theimportant consideration is relative, rather than absolute retentiontimes. Thus it is known that in a homologous series the ratio ofretention times is constant from one member to the next.

RETENTION TIMES AT 170 C.

Retention Retention times relative to air.

Retention time divided by that of next lower homolog.

It is evident from the data above that the effect of an added D unit ina methoxysiloxanol is almost identical to its effect in the known seriesof cyclic siloxanes. This regularity provides an invaluable aid toidentification. The same is not true in the series HOD' H, CH OD H, C HOD H, C3H7OD3H, in which the homologous change involves a relativelysmall part of the molecule.

RETENTION TIMES AT 190 C.

Retention time,

Compound:

CHaOD iH EXAMPLE 13 A. One hundred parts of a silicone gum (containing0.1 percent of methylvinylsiloxane) was mixed with parts of CH OD- H and36 parts of fumed silica (Cab-O- Sil PIS-5) in a Sigma mixer at 250 F.No difliculty was encountered and a smooth compound was obtained.

B. A similar compound was prepared with only 6 parts of CH OD H. Somemixing ditficulty was encountered, but a smooth compound was eventuallyobtained.

C. A reference compound was prepared from 100 parts of the same gum, 16parts of a standard softener (antistructure agent) composed of a linearpolydimethylsilox- A B C Hardness, Shore A Tensile strength, p.s.iElongation, percent Compression set (ASTM D395 Method B) 4s 52 50 1, 2001, 000 1, 475 400 500 23 18 so It can be seen from these data that thephysical properties are approximately equivalent, in general. However,the better (lower) compression set values of the elastomers containingthe methoxysiloxanol are clearly evident.

EXAMPLE 14 Six drops of CH OD H were applied to the surface of a cleanglass plate. After 10 minutes at room temperature the surface was washedoff with acetone and found not to be water repellent. A second glassplate was treated with six drops of CH OD H and heated 15 minutes at C.The liquid had evaporated and the surface was found to be somewhat waterrepellent; water drops on the surface formed a contact angle of about60. A third glass plate was treated with 6 drops of CH OD H and heatedfor 30 minutes at 150 C., whereby it became water repellent; water dropsformed contact angles of about 70 on the surface.

EXAMPLE 15 A fumed silica (Cab-O-Sil MS-7) was mixed with one tenth itsweight of CH O'D H and allowed to stand for 16 hours at roomtemperature. It was not visibly altered and was easily dispersed inwater. A similarly treated silica heated for one hour at C. in a closedcontainer became highly hydrophobic and could not be dispersed in water.

EXAMPLE 16 A precipitated calcium polysilicate (Hi-Sil 404) (1.0 part)Was heated with 0.15 part of CH OD H in a closed bottle at 95 C. for twohours, at the end of which it was completely hydrophobic.

Although specific examples are mentioned and have been herein described,it is not intended to limit the invention solely thereto but to includeall the variations and modifications falling within the spirit and scopeof the appended claims.

The invention claimed is:

1. Alpha-alkoxy-omega-siloxanols having the formula R'O(R SiO) H, inwhich R is selected from the group consisting of a monovalenthydrocarbon radical, a halogenated monovalent hydrocarbon radical and acyanoalkyl radical having up to 8 carbon atoms, R is a radical derivedfrom a primary or secondary alcohol and is selected from the groupconsisting of alkyl radicals, cycloalkyl radicals, alkenyl radicals,aralkyl radicals and substituted derivatives thereof having up to 20carbon atoms, and x is a integer of from 2 to 10.

2. The alpha-alkoxy-omega-siloxanols of claim 1, in which at least 50percent of the R radicals are methyl, R is an alkyl radical of up tofour carbon atoms, and x is an integer of from 3 to 5.

3. The composition of claim 2 wherein the alphaalkoxy-omega-siloxanol is5-methoxyhexamethyltrisilox an-l-ol.

4. The composition of claim 2 wherein the alphaalkoxy-omega-siloxanol is7-methoxyoctamethyltetrasiloxan-l-ol.

5. The composition of claim 2 wherein the alphaalkoxy-omega-siloxanol is9-methoxydecamethylpentasiloxan-l-ol.

6. The composition of claim 2 wherein the alphaalkoxy-omega-siloxanol isS-methoxy-1,3,5-trimethyl-1,3, 5-trivinyltrisiloxan-1-ol.

7. A method for preparing an alpha-alkoxy-omegasiloxanol having theformula RO(R SiO) H which comprises reacting a cyclic polysiloxane witha primary or secondary alcohol of the formula R'OH in which R isselected from the group consisting of a monovalent hydrocarbon radical,a halogenated monovalent hydrocarbon radical and a cyanoalkyl radicalhaving up to 8 carbon atoms, R is selected from the group consisting ofalkyl radicals, cycloalkyl radicals, alkenyl radicals, aralkyl radicalsand substituted derivatives thereof having up to 20 carbon atoms and xis an integer of from 2 to in a mol ratio of alcohol to cyclicpolysiloxane of at least 2:1 and at temperatures up to the refluxtemperature of the alcohol.

8. The method of claim 7 in which the cyclic polysiloxane has theformula (R SiO) in which R is selected from the group consisting of ahydrocarbon radical, a halogenated monovalent hydrocarbon radical and acyanoalkyl radical having up to 8 carbon atoms and y is an integer offrom 3 to 10.

9. The method of claim 8 in which a catalyst is added, said catalysthaving a 13K, or pK value of from 1.5 to 10.

10. The method of claim 9 in which the catalyst is formic acid.

11. The method of claim 9 in which the catalyst is acetic acid.

12. The method of claim 9 in which the catalyst is ammonia.

References Cited UNITED STATES PATENTS 3,541,126 11/1970 Baronnier eta1. 260448.8 R 2,842,522 7/1958 Frye 260448.8 R X 3,296,198 1/1967 Lukes260448.8 R X 2,826,599 3/1958 Meals 260448.8 R 2,746,982 5/1956 Hyde260448.8 R

DANIEL E. WYMAN, Primary Examiner P. F. SHAVER, Assistant Examiner US.Cl. X.R.

117121, 123 D, 126 GS; 26037 SB

